1. Field of the Invention
This invention relates generally to slide fasteners and particularly to coupling elements therefor. More particularly, the invention is directed to such coupling elements which have a cross-sectionally semi-circular configuration and which are formed into a continuous meandering structure.
2. Prior Art
Slide fasteners having coupling elements of the character described find wide application as closure devices for garment articles, bags, suitcases, coverings and the like. Coupling elements having a semi-circular transverse cross-section formed from a synthetic resinous monofilament into a meandering or zig-zag structure are already known as disclosed for example in Japanese Pat. Publication No. 39-9390 (corresponding to U.S. Pat. No. 2,919,482).
Due to its physical peculiarity of being sectionally semi-circular and hence relatively small in radius, the monofilament is difficult to be freely bent or otherwise formed into a meandering structure with its flat surface aligned in a common plane and without causing the monofilament to become wavy or run off a predetermined track on opposite surfaces of a stringer tape. This makes it difficult to pass the sewing threads properly on the monofilament and through the tape. Furthermore, the monofilament being sectionally semi-circular provides limited contact areas to be guidedly threaded through a slider and hence opposed rows of coupling elements made from such monofilament would fail to be brought securely together, or would undergo what is known as "chain crack". Improper or loose coupling condition of the coupling elements would also lead to their deformation or damage when jammed between the stringer tape and the slider flanges.